The invention pertains to the field of electronic thermometers and more particularly the field of fast response electronic thermometers employing a sensor probe.
Electronic thermometers are widely used in the healthcare field for measuring a patient's body temperature. Typical electronic thermometers have the form of a probe with an elongated shaft. Electronic temperature sensors such as thermistors or other temperature sensitive elements are contained within the shaft portion. In one version, the probe includes a cup-shaped aluminum tip at its free end. A thermistor is placed in thermal contact with the aluminum tip inside the probe. When a free end portion is placed, for example, in a patient's mouth, the tip is heated up by the patient's body and the thermistor measures the temperature of the tip. Additional electronics connected to the electronic sensor components may be contained within a base unit connected by wire to the shaft portion or may be contained within a handle of the shaft portion, for example. Electronic components receive input from the sensor components to compute the patient's temperature. The temperature is then typically displayed on a visual output device such as a seven segment numerical display device. Additional features of known electronic thermometers include an audible temperature level notification such as a beep or tone alert signal. A disposable cover or sheath is typically fitted over the shaft portion and disposed after each use of the thermometer for sanitary reasons.
Electronic thermometers have many advantages over conventional thermometers and have essentially replaced the use of conventional glass thermometers in the healthcare field. One advantage of electronic thermometers over their conventional glass counterparts is the speed at which a temperature reading can be taken. Several procedures are used to promote a rapid measurement of the subject's temperature. One technique employed is to use predictive algorithms as part of thermometer logic to extrapolate the temperature measurements from the thermistor in contact with the tip to arrive at a temperature reading in advance of the tip reaching equilibrium with the body temperature. Another technique that can be employed simultaneously with a predictive algorithm is to heat the probe to near the body temperature so that part of the probe away from the tip does not act as a heat sink, allowing the tip to reach a temperature close to the body temperature more rapidly. Heating can be accomplished by a resistor placed in contact with the probe. Another thermistor may be placed in contact with the probe to measure the amount the resistor is heating the probe, which is used to control the heating. It is also known to use an isolator to reduce heat loss from the tip to other parts of the probe. Co-assigned U.S. Pat. No. 6,839,651 discloses the use of such an isolator and is incorporated herein by reference.
To assemble the probe, the circuitry (e.g., the thermistors and resistor) is mounted on a flexible substrate that supports and provides electrical connection for the components. The combination of the components and the flexible substrate is commonly called a “flex circuit”. The substrate may be initially flat to facilitate ease of mounting the components, but can be bent into position upon assembly into the probe. More specifically, the flexible substrate is bent to place one thermistor in position for contacting the probe tip, and to place the resistor and other thermistor in contact with a separator adjacent the probe tip. These components can be glued in place with a thermally conductive adhesive in the final assembly. However, before the adhesive is brought into contact with the components and/or before the adhesive sets, the components may undesirably move. The result of motion can be insufficient contact of the components with the tip and/or separator to heat or sense temperature in the final assembly. Preferably, such assembly failures should be minimized or avoided, and a highly repeatable assembly process is achieved.